Anyone who loves cars will be delighted when you present them with a car-shaped birthday cake. Clip a picture of the car you want to base the cake on, and use it to carve the cake to your liking. Using frosting, cookies and candy as adornments for your car's details makes it completely edible. You don't need to be a professional pastry chef to make your cake look like an automobile -- with some creativity and patience, you'll end up with a sweet masterpiece.
Place the 20-by-20-cm (8-by-8-inch) cake on top of the sheet cake, 7.5 cm (3 inches) from the right end. The square cake will be the dome of the car. The left side of the sheet cake will be the hood, and the right side of the cake will be the bumper.
Use your knife to carve out the bonnet of the car. Newer cars have more of a curve, whereas older cars are boxier, so it's a good idea to keep a photo of the car you're emulating nearby. Cut an angle into the left side of the square cake to make a windshield. Do the same to the right side of the square cake if you want to make the back window slanted as well.
Dye your frosting with food colouring to your desired car colour, and frost the entire cake. Reserve 60 ml (1/4 cup) of frosting. Use a frosting knife to make the frosting smooth.
Attach your round chocolate cookies to the sides of the car where the tyres would be. Use the extra frosting to adhere the cookies to the cake.
Cut two 3.75-by-15-cm (1.5-by-6-inch) pieces of gelatin sheets for your front and back windows and four 4-by-5-cm (1.5-by-2-inch) pieces for your side windows. Frost the back sides completely with the reserved frosting, and then adhere them to the car.
Use small yellow candies, such as M&Ms, Skittles or gumdrops, as headlights and tail lights. Use the reserved frosting to attach them to the front and back of the car. Pipe on any words or numbers as you see fit.
You may swap the frosting for fondant for a smoother look.